Numerous water wheels and rotors have been developed for use in streams incorporating various hinged flap arrangements to cause the wheel to rotate in one direction only and minimize counter forces due to reverse relative currents. Because these units were designed to be used in streams and rivers wherein the prevailing current is always in the same direction, none of the horizontal-axled wheels are designed to effectively extract power from the water regardless of the direction of the prevailing current, which would be necessary in the event of employment of the units in a tide-water environment.